Influence of fluid velocities on the degradation of volatile aromatic compounds in membrane bound biofilms

Abstract

In a cylindrical laboratory reactor, in which a biofilm was grown on a gas-permeable silicone membrane tubing through which oxygen was supplied, the removal of xylene from the bulk fluid was investigated. Two days after starting the experiment 98 % of xylene was degraded and was no longer transferred into the gas phase. Using polarographic microelectrodes the thickness of the biofilm and the boundary layer as well as the oxygen profiles in both layers have been measured. The fluid velocity had three major influences: it affected the boundary layer thickness, the biofilm density and the sloughing of the biofilm. At higher fluid velocities (Reynolds numbers) high oxygen consumption within the biofilm could be quantified. At these higher fluid velocities the biofilm was grown with a higher density and adhered better to the membrane. By application of higher oxygen partial pressures in the gas phase and higher fluid velocities in the liquid phase, the mean degradation efficiency was increased from 38 to 96 %. A computer simulation showed good correspondence with the experimental investigations and allowed a total process analysis. Membrane-biofilm reactors are preferred for technical applications as, e.g., treatment of landfill leachates with high contents of volatile organics.